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150+ Switch Gear and Protection Solved MCQs

These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .

1.

The main function of a fuse is to

A. protect the line
B. open the circuit
C. protect the appliance
D. prevent excessive currents
Answer» D. prevent excessive currents
2.

On which of the following routine tests are conducted?

A. Oil circuit breakers
B. Air blast circuit breakers
C. Minimum oil circuit breakers
D. All of the above
Answer» D. All of the above
3.

SF6 gas

A. is yellow in colour
B. is lighter than air
C. is nontoxic
D. has pungent small
Answer» C. is nontoxic
4.

The arcing contacts in a circuit breaker are made of

A. copper tungsten alloy
B. porcelain
C. electrolytic copper
D. aluminium alloy
Answer» A. copper tungsten alloy
5.

Which of the following medium is employed for extinction of arc in air circuit breaker ?

A. Water
B. Oil
C. Air
D. SF6
Answer» C. Air
6.

With which of the following, a circuit breaker must be equipped for remote operation ?

A. Inverse time trip
B. Time-delay trip
C. Shunt trip
D. None of the above
Answer» C. Shunt trip
7.

Fault diverters are basically

A. fuses
B. relays
C. fast switches
D. circuit breakers
Answer» C. fast switches
8.

A thermal protection switch can protect against

A. short-circuit
B. temperature
C. overload
D. over voltage
Answer» C. overload
9.

Arc in a circuit behaves as

A. a capackive reactance
B. an inductive reactance
C. a resistance increasing with voltage rise across the arc
D. a resistance decreasing with voltage rise across the arc
Answer» D. a resistance decreasing with voltage rise across the arc
10.

Thermal circuit breaker has

A. delayed trip action
B. instantaneous trip action
C. both of the above
D. none of the above
Answer» A. delayed trip action
11.

Relays can be designed to respond to changes in

A. resistance, reactance or impedance
B. voltage and current
C. light intensity
D. all above
Answer» D. all above
12.

Overload relays are of…… type.

A. induction
B. solid state
C. thermal
D. all above
Answer» D. all above
13.

Thermal overload relays are used to protect the motor against over current due to

A. short-circuits
B. heavy loads
C. grounds
D. all of the above
Answer» B. heavy loads
14.

Magnetic circuit breaker has ______ trip action.

A. delayed
B. instantaneous
C. both of the above
D. none of the above
Answer» B. instantaneous
15.

D.C. shunt relays are made of

A. few turns of thin wire
B. few turns of thick wire
C. many turns of thin wire
D. many turns of thick wire
Answer» C. many turns of thin wire
16.

The relay operating speed depends upon

A. the spring tension
B. the rate of flux built up
C. armature core air gap
D. all of the above
Answer» D. all of the above
17.

In order that current should flow without causing excessive heating or voltage drop, the relay contacts should

A. have low contact resistance
B. be clean and smooth
C. be of sufficient size and proper shape
D. have all above properties
Answer» D. have all above properties
18.

Circuit breakers usually operate under

A. transient state of short-circuit current
B. sub-transient state of short-circuit current
C. steady state of short-circuit current
D. after D.C. component has ceased
Answer» A. transient state of short-circuit current
19.

Circuit breakers are essentially

A. current carrying contacts called electrodes
B. arc extinguishers
C. circuits to break the system
D. tr
Answer» A. current carrying contacts called electrodes
20.

The current zero interruption, in oil and air blast circuit breakers, is achieved by

A. lengthening of the gap
B. cooling and blast effect
C. both (a) and (b)
D. deionizing the oil with forced air
Answer» C. both (a) and (b)
21.

Air blast circuit breaker is used for

A. over currents
B. short duty
C. intermittant duty
D. repeated duty
Answer» D. repeated duty
22.

An efficient and a well designed protective relaying should have

A. good selectivity and reliability
B. economy and simplicity
C. high speed and selectivity
D. all of the above
Answer» D. all of the above
23.

Burden of a protective relay is the power

A. required to operate the circuit breaker
B. absorbed by the circuit of relay
C. developed by the relay circuit
D. none of the above
Answer» B. absorbed by the circuit of relay
24.

Directional relays are based on flow of

A. power
B. current
C. voltage wave
D. all of the above
Answer» A. power
25.

A differential relay measures the vector difference between

A. two currents
B. two voltages
C. two or more similar electrical quantities
D. none of the above
Answer» C. two or more similar electrical quantities
26.

A transmission line is protected by

A. inrush protection
B. distance protection
C. time graded and current graded over current protection
D. both (b) and (c)
Answer» D. both (b) and (c)
27.

Large internal faults are protected by

A. merz price percentage differential protection
B. mho and ohm relays
C. horn gaps and temperature relays
D. earth fault and positive sequence relays
Answer» A. merz price percentage differential protection
28.

When a transmission line is energized, the wave that propagates on it is

A. current wave only
B. voltage wave only
C. both (a) and (b)
D. power factor wave only
Answer» C. both (a) and (b)
29.

Protective relays are devices that detect abnormal conditions in electrical circuits by measuring

A. current during abnormal condition
B. voltage during abnormal condition
C. constantly the electrical quantities which differ during normal and abnormal conditions
D. none of the above
Answer» C. constantly the electrical quantities which differ during normal and abnormal conditions
30.

The voltage appearing across the contacts after opening of the circuit breaker is called______voltage.

A. recovery
B. surge
C. operating
D. arc
Answer» A. recovery
31.

Ionization in circuit breaker is facilitated by

A. high temperature
B. increase of mean free path
C. increasing field strength
D. all of the above
Answer» D. all of the above
32.

In a circuit breaker the basic problem is to

A. maintain the arc
B. extinguish the arc
C. transmit large power
D. emit the ionizing electrons
Answer» C. transmit large power
33.

Overheating of relay contacts or contact born out is due to

A. slow making and breaking of load circuit contacts
B. foreign matter on the contact surface
C. too low contact pressure
D. all of the above
Answer» D. all of the above
34.

Interruption of large currents by relay requires

A. arc suppressing blow out coils
B. wide separation of the opened contacts
C. high speed opening of contacts
D. all of the above
Answer» D. all of the above
35.

Shunt capacitance is neglected while considering

A. short transmission line
B. medium transmission line
C. long transmission line
D. medium and long tr
Answer» A. short transmission line
36.

The arc voltage produced in A.C. circuit breaker is always

A. in phase with the arc current
B. lagging the arc current by 90″
C. leading the arc current by 90°
D. none of the above
Answer» A. in phase with the arc current
37.

The time of closing the cycle, in modern circuit breakers is

A. 0.003 sec
B. 0.001 sec
C. 0.01 sec
D. 0.10 sec
Answer» A. 0.003 sec
38.

Insulation resistance of high voltage circuit breakers is more than

A. 1 mega ohms
B. 10 mega ohms
C. 100 mega ohms
D. 500 mega ohms
Answer» C. 100 mega ohms
39.

H.R.C. fuses provide best protection against

A. overload
B. reverse current
C. open-circuits
D. short-circuits
Answer» D. short-circuits
40.

The ground wire should not be smaller than No ______ copper.

A. 2
B. 4
C. 6
D. 10
Answer» D. 10
41.

The delay fuses are used for the protection of ________ .

A. motors
B. power outlet circuits
C. fluorescent lamps
D. light circuits
Answer» A. motors
42.

Which of the following is the least expensive protection for overcurrent is low voltage system ?

A. Rewireable fuse
B. Isolator
C. Oil circuit breaker
D. Air break circuit breaker
Answer» A. Rewireable fuse
43.

Resistance grounding is used for voltage between

A. 33kVto66kV
B. HkVto33kV
C. 3.3kVandllkV
D. none of the above
Answer» C. 3.3kVandllkV
44.

The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to

A. lubricate the contacts
B. insulate the contacts from switch body
C. extinguish the arc
D. all of the above
Answer» C. extinguish the arc
45.

In Railway applications ______ circuit breaker is used.

A. SFe
B. bulk oil
C. minimum oil
D. air break
Answer» D. air break
46.

To protect most of the electrical equipment handling low power, the types of relays used are

A. thermocouple
B. electronic and bimetallic
C. both (a) and (b)
D. none of the above
Answer» C. both (a) and (b)
47.

Wave trap is used to trap waves of

A. power frequencies
B. higher frequencies entering generator or transformer units
C. either of the above
D. none of the above
Answer» B. higher frequencies entering generator or transformer units
48.

Ungrounded neutral transmission system is not recommended because of system

A. insulation being overstressed due to over voltages
B. insulation overstress may lead to failure and subsequent phase to phase faults
C. being inadequately protected against ground fault
D. all of the above
Answer» D. all of the above
49.

The reflection co-efficient at the open circuited end of a transmission line.

A. zero
B. infinity
C. unity
D. none of the above
Answer» C. unity
50.

For the protection of power station buildings against direct strokes the requirements are

A. interception
B. interception and conduction
C. interception, conduction and dissipation
D. interception, conduction, dissipation and reflection
Answer» C. interception, conduction and dissipation

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